Flow pack machines for the manufacture, filling and welding of film tubes are known both as continuous and clocked operating machines. In the case of continuously operating flow pack machines tube transfer takes place continuously without any stoppage and pack welding takes place with the film tube moving. However, in the case of clocked operating flow pack machines, transverse welding of the pack takes place with the film tube stationary. Longitudinal welding of the pack can take place with the film tube stationary or moving.
The transverse welding of the pack takes place by means of transverse sealing jaws, whilst in the case of flow pack machines with a clocked operation there is only a movement of the transverse sealing jaws towards and away from one another perpendicular to the film tube. In the case of vertical flow pack machines with a continuous operation, the transverse sealing jaws are moved along predetermined paths from a lower-lying welding location to a higher-lying welding location on the film tube and then moves downwards together with said film tube, performing the welding process.
In order to maintain the transverse sealing jaws on this path curve, EP-Bl-368 095 discloses a flow pack machine, in which the transverse sealing jaws are in each case guided in rotating manner on a closed, substantially circular curved sector or cam path, which is linear on the side facing the film tube. As a result, in the vicinity of the linear curved sector, the film tube is engaged and guided downwards by the parallel oriented clamping surfaces of the transverse sealing jaws, the clamping surfaces being kept parallel to one another by the curved sector throughout the sealing period. As the film tube is consequently clamped on a very long, straight path between the transverse sealing jaws, this permits a reliable sealing of difficultly processable materials. However, it is disadvantageous that the transverse sealing jaw on passing between circular and straight curved sectors is so bent with respect to the film tube that the transverse sealing jaws initially only engage with their edges on the film, so that there is an extremely high risk of overheating of the film tube in this area.
Therefore flow pack machines have been provided, in which the transverse sealing jaws are only displaced parallel to themselves throughout the rotary movement, so that their welding faces always face the film tube. Such a flow pack machine is known from German patent 27 51 928. The transverse sealing jaws are resiliently mounted on continuously rotating wheels, each wheel having three parallel disks and the jaw holders are mounted between two equiaxially arranged disks with aligned hearing points, whilst the third disk with a displaced shaft is arranged adjacent to one of the two disks and forms the displaced bearing point of the jaw holder. By means of the said two oppositely displaced bearing points the transverse sealing jaws perform a purely translatory movement and are maintained in this movement, so that they are always oriented parallel to themselves and in particular in the horizontal position. Consequently there are no relative pivoting movements of the sealing elements and their carriers, so that from the outset the transverse sealing jaws engage with their entire heating surface on the film tube and there is no burning of the film tube material. In order to transfer the rotary movement to the mechanism comprising wheels and transverse sealing jaws on the opposite side of the film tube, the disks forming the bearing points for the jaw holder mesh with the disks of the opposing mechanism. As a result of an elastic sleeve or sliding bearing of the sealing parts of the transverse sealing jaws by means of a compression spring the necessary sealing pressure is applied to the film tube to be sealed.
It is disadvantageous in this intrinsically satisfactorily operating flow pack machine that a complicated construction is necessary for ensuring the maintaining parallel of the transverse sealing jaws and for transferring the rotary movement to the opposite sealing mechanisms. As a result of the fact that e.g. several disks mesh with one another for the transfer of the rotary movement, it is not possible to easily modify the pivot pins of both sealing mechanisms. The same applies with respect to the replacement of the mutually meshing disks in the case of damage, particularly since within said disks are located the bearing points for the jaw holders and consequently the transverse sealing jaws. In the case of different materials for the film tube it is also not easily possible to adjust the contact pressure, because the sealing mechanism is supported by means of the spring on a plunger, which is guided in the jaw holder and equipped with a roller, which engages with a fixed cam located in the area of the vertical working section and which maintains stationary the plunger and consequently the sealing mechanism in the horizontal direction, which leads to a constant pressure of the sealing part of the transverse sealing jaw. In the case of other web materials it is then necessary to interchange the cams and/or at least the springs, in order to be able to correspondingly adapt the sealing pressure.
The problem of the invention is consequently to so improve a flow pack machine of the aforementioned type that, with a simplified construction and operationally reliable functioning, the maintaining parallel of the heating surfaces of the transverse sealing jaws is ensured over the entire circular path and there is a precise guidance thereof in the area of the working section.